Binary Stars

Binary star is a system of two stars that revolve around one another. Binary (triple and multiple) stars are very common, astronomers calculated that nearly half of all stars are members of multiple systems. The nearest star system, Alpha Centauri is actually our nearest example of a multiple star system. It consists of three stars - two similar to the Sun and one dim, small, red star - orbiting each other.
Binary stars is gravitationally bound system of two stars that are moving around a common center of mass in elliptical orbits. Star more massive and closer to the center of mass is the primary and the other is the secondary. The primary star has also a stronger glow.

Two-thirds of all stars are part of multiple star systems, where two or more stars are born at the same time from the same gas cloud. Only about 30% of all stars are single, like the Sun. The distances between companion stars nranges from less than 10 million miles (0.1 AU), to over 10,000 AU. Similarly, the time it takes stars to orbit each other varies from a few hours to a million years or more.
New theoretical work shows that gas-giant planet formation can occur around binary stars in much the same way that it occurs around single stars like the Sun.